The present invention relates to an air conditioning system having air quantity regulating devices for air intake and exhaust, and more specifically to an air conditioning system having a charging blower and a discharging blower and adapted to perform air intake and exhaust through ducts connected to an air conditioner.
In a conventional air conditioning system, a damper for regulating the incoming outside air quantity is disposed in a duct which connects an outside air intake port and an air conditioner, and another damper for regulating the exhaust air quantity is disposed in a duct which connects a discharging blower and an exhaust port.
Hereupon, part of the air discharged from an air conditioning zone by the discharging blower is circulated into the air conditioning zone without being exhausted. To attain this, another duct is used to connect the air conditioner and the middle portion of the duct which connects the discharging blower and the discharging air quantity regulating damper. Since the pressure difference between the discharging blower and the air conditioner is very large, an additional air quantity regulating damper is provided in the duct for circulation.
In such air quantity regulating process, the quantity of required air is detected as the air flows through the opening of the damper, based on a damper characteristic (pressure difference-air quantity characteristic) which is obtained under predetermined conditions. In an ordinary air conditioning system, however, it is difficult to maintain a constant pressure difference between specified regions. In operations for outside air intake and exhaust, in particular, the conditions or circumstances surrounding the outside air intake port and exhaust port vary with the changes of the direction and speed of the wind outside the building in which the air conditioning system is installed. Also, the conditions may change according to the degree of contamination of an air filter attached to the air conditioner. In an air conditioning system of a variable air quantity type, moreover, charging and discharging air quantities change with fluctuations of load in the air conditioning zone. Thus, the changes in pressure applied to the outside air intake port and exhaust port are very great even if the charging and discharging blowers are controlled.
These circumstances indicate that proper air quantity control can be achieved only by detecting the pressure condition for every moment and controlling the opening of the air quantity regulating damper while weighting the detected pressure condition against the damper characteristic.
However, it costs too high to be practical to control the damper opening by detecting and calculating several variable factors every moment for the regulation of the incoming air outside air quantity and exhaust air quantity.
These prior art control methods cannot practically achieve accurate air quantity regulation, raising the following problems.
(1) If the incoming outside air quantity is larger than a set value, air conditioning load will increase.
(2) If the incoming outside air quantity is smaller than a set value, a draft entering the air conditioning zone through a door or window sill increase, so that the air conditioning load will increase.
(3) If the exhaust air quantity is smaller than a set value, a foul smell and poisonous gas in the air conditioning zone will increase to spoil environment.
(4) If the incoming outside air quantity is not equal to the exhaust air quantity, well-balanced air conditioning in the air conditioning zone can not be achieved.
These problems have been ignored as insignificant for air conditioning systems of a single- or dual-duct constant air quantity type. However, they are expressly significant for air conditioning systems of a single-duct variable air quantity type.